Laser beam welding is a technique for irradiating a workpiece (for example, two steel plates) with a laser beam to locally melt and solidify the workpiece, thereby joining the workpiece. In the laser beam welding apparatus, for example, a welding point is checked as a laser beam welding inspection based on a reflected light from a welded portion of the workpiece (for example, see JP-A 2011-167697).
Recently, in welding of vehicle body, remote laser beam welding is performed even in spot welding. The remote laser beam welding is a technique for scanning a portion to be welded with a long-focus laser beam using a mirror to weld the portion.
In the remote laser beam welding, multi-step laser beam irradiation such as irradiation of a laser beam for welding and irradiation of a laser beam for inspection is performed in one welding point (a step for welding one spot). Therefore, the beginning and the end of the one welding point are hardly detected based on only turning on/off of irradiation of a laser beam.